Invalid update: invalid number of rows in section 0 with NSFetchedResultsController - ios

Question

I have 2 ViewControllers:
VC1 populates its tableView based on CoreData attribute isPicked, which is bool and show only items with true state. VC2 is a second Modal (not Full Screen) View Controller which allow user to change the state of isPicked attribute: check and uncheck item (make it true or false). The idea is user picks needed items end dismiss the VC2 and the items should appear in VC1.
I have implemented NSFetchedResultsController to both VC1 and VC2. And as soon as I press on first item (i.e. change isPicked state to true) I receive the error from VC1:
[error] fault: Serious application error. An exception was caught from the delegate of NSFetchedResultsController during a call to -controllerDidChangeContent:. Invalid update: invalid number of rows in section 0. The number of rows contained in an existing section after the update (2) must be equal to the number of rows contained in that section before the update (1), plus or minus the number of rows inserted or deleted from that section (0 inserted, 0 deleted) and plus or minus the number of rows moved into or out of that section (0 moved in, 0 moved out).
Here is how I change a state of item in VC2 (true\false):
override func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
guard let currencyArray = fetchedResultsController.fetchedObjects else { return }
let cell = tableView.cellForRow(at: indexPath) as! PickCurrencyTableViewCell
for currency in currencyArray {
if currency.shortName == cell.shortName.text {
currency.isPicked = !currency.isPicked
coreDataManager.save()
}
}
}
Here is my VC1 NSFetchedResultsController implementation:
override func viewDidLoad() {
super.viewDidLoad()
setupFetchedResultsController()
}
func setupFetchedResultsController() {
let predicate = NSPredicate(format: "isForConverter == YES")
fetchedResultsController = createCurrencyFetchedResultsController(and: predicate)
fetchedResultsController.delegate = self
try? fetchedResultsController.performFetch()
}
func createCurrencyFetchedResultsController(with request: NSFetchRequest<Currency> = Currency.fetchRequest(), and predicate: NSPredicate? = nil, sortDescriptor: [NSSortDescriptor] = [NSSortDescriptor(key: "shortName", ascending: true)]) -> NSFetchedResultsController<Currency> {
request.predicate = predicate
request.sortDescriptors = sortDescriptor
return NSFetchedResultsController(fetchRequest: request, managedObjectContext: context, sectionNameKeyPath: nil, cacheName: nil)
}
Here is my VC1 NSFetchedResultsController delegate:
extension VC1: NSFetchedResultsControllerDelegate {
func controllerWillChangeContent(_ controller: NSFetchedResultsController<NSFetchRequestResult>) {
tableView.beginUpdates()
}
func controllerDidChangeContent(_ controller: NSFetchedResultsController<NSFetchRequestResult>) {
tableView.endUpdates()
}
func controller(_ controller: NSFetchedResultsController<NSFetchRequestResult>, didChange anObject: Any, at indexPath: IndexPath?, for type: NSFetchedResultsChangeType, newIndexPath: IndexPath?) {
if let indexPath = indexPath, let newIndexPath = newIndexPath {
switch type {
case .update:
tableView.reloadRows(at: [indexPath], with: .none)
case .move:
tableView.moveRow(at: indexPath, to: newIndexPath)
case .delete:
tableView.deleteRows(at: [indexPath], with: .none)
case .insert:
tableView.insertRows(at: [indexPath], with: .none)
default:
tableView.reloadData()
}
}
}
}
When I reload the app, picked item shows itself in VC1 (which caused crash). But every change in VC2 crashes the app again with the same error. I don't have any methods to delete items in VC1 or so. I need that VC1 tableView just show or hide items according to isPicked state made from VC2.
What I missed in my code?
UPDATE: my VC1 TableView methods
override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
let currency = fetchedResultsController.sections![section]
return currency.numberOfObjects
}
override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCell(withIdentifier: "converterCell", for: indexPath) as! ConverterTableViewCell
let currency = fetchedResultsController.object(at: indexPath)
cell.shortName.text = currency.shortName
cell.fullName.text = currency.fullName
return cell
}

Answer 1

Doc states:
controller(_:didChange:at:for:newIndexPath:)
indexPath
The index path of the changed object (this value is nil for
insertions).
So, you should change the code like this:
func controller(_ controller: NSFetchedResultsController<NSFetchRequestResult>, didChange anObject: Any, at indexPath: IndexPath?, for type: NSFetchedResultsChangeType, newIndexPath: IndexPath?) {
switch type {
case .update:
if let indexPath = indexPath {
tableView.reloadRows(at: [indexPath], with: .none)
}
case .move:
if let indexPath = indexPath {
tableView.moveRow(at: indexPath, to: newIndexPath)
}
case .delete:
if let indexPath = indexPath {
tableView.deleteRows(at: [indexPath], with: .none)
tableView.reloadData() // << May be needed ?
}
case .insert:
if let newIndexPath = newIndexPath {
tableView.insertRows(at: [newIndexPath], with: .none)
tableView.reloadData() // << May be needed ?
}
default:
tableView.reloadData()
}
}
}